Lubricant compositions having improved corrosion and oxidation properties



. properties. i and .various phenolic antioxidants have been employed,

United States Patent Ofifice 3,296,135 Patented Jan. 3, 1967 Thisinvention relates to synthetic lubricating oil compositions which exhibit improved resistance to corrosion and; oxidation and which, in addition, possess a high degree ofthermal stability. More particularly, this invention is. directed to synthetic lubricant compositions which meet thecritical test standards required of turboprop and turbojetlubricants.

; perature encountered and allow increased engine operating :temperatures. However, the synthetic ester fluids employed as lubricants may be corrosive toward metal,

particularly at high temperatures. Itis immediately ap- 'parent thatserious damage can occur to vital parts of an engine by permitting such corrosion to continue unchecked! Turbopropuand turbojet lubricants are required to meet certain critical viscosity requirements as set forth inl specific test specifications. The critical turbojet standards for the military are set forth in U.S. Military Specification Mil-7808B. .Turboprop lubricant specifications for. commercial. aircraft are described by the Allison Division Specification EMS-35F and the British Ministry of Supply Specification D. Eng. RD. 2487, Issue 3. The British ispecification demands a very high degree of thermalwstability as it requires the lubricant to exhibit satisfactory viscosity stability after exposure to temperatures ashigh as 536 F.

Inuthe adaptation of synthetic lubricants such as those hereinbefore:discussed, it has often been found necessaryto modify the fluids with additives to improve their For this purpose, amine-type antioxidants depending upon thexparticular use intended for the lubricant. I The. aforesaid vigorous standards demanded of turbojet and; .turbopropdubricants have been a barrier to .theiientry of uninhibited ester fluids into this field. This has prompted investigations to find a suitable additive .system3which will enable these synthetic base fluids to comply with the turboprop and turbojet lubricant specifications.

Accordingly it is an object of the present invention to provideua novel. additive system which will impart to synthetic base fluids, high resistance to corrosion and oxidation.

Itiiis a further. object of the invention to modify said 1 novel additive system to prevent thermal degradation .novelallubricating composition which may be used in turbojet andlturboprop engines.

It is a still further object of the invention to provide such a novellubricant which will meet the requirements demanded of advanced high temperature synthetic lubricants as exemplified by the Allison Test and the British Ministry of Supply Test.

In accordance with the present invention, it has been found that improved non-oxidative and non-corrosive properties may be achieved in synthetic lubricating compositions, by the addition thereto of a novel additive system which system comprises at least one amine antioxidant, at least one phenolic antioxidant, and a metal corrosion inhibitor of the formula:

own

wherein R represents hydrogen or an alkyl group having from 1 to 4 carbon atoms.

In a particular embodiment of this invention the said novel additives system may be modified to obtain thermal stability at temperatures in excess of 500 F. by addition thereto of certain condensed ring compounds as thermolysis additives. These thermolysis additives are particularly useful in lubricating compositions which must pass the high temperature requirements of the British Ministry of Supply Test. At such high temperatures as are present in this test, it has been found that molecular degradation of the synthetic lubricant fluid will take place even under non-oxidizing conditions, e.g., in oxygenfree environments. The compounds herein designated as thermolysis additives have been found to be extremely effective to prevent such high temperature degradation.

The amine antioxidants which are suitable for use in the novel additive package of this invention include phenothiazine, N-methylphenothiazine, N-phenyI-a-naphthylamine, N-phenyl-B-naphthylamine, p-phenylenediamine, o-phenylenediamine, 2,4'-diaminodiphenylamine, a,{3-dinaphthylamine, 3,7-dioctylphenothiazine, p,p'dioctyldiphenylamine and the like. Preferred amine antioxidants are phenothiazine, N-methylphenothiazine, N-phenyl-anaphthylamine, and N-phenyl-B-naphthylamine. Eminently preferred are phenothiazine and N-phenyl-a-naphthylamine.

The phenolic antioxidants which are useful in the novel additive package are 2,6-di-t-buty1-4-methylphenol, 2,6- di-t-butyl-4-benzylphenol, 3-t-butyltetrahydro-2-naphthol, 6-butyl-5-indanol, diphenylol propane, 2-2'-methylene-bis (4-ethyl-6-t-butylphenol), 4,4-methylene-bis(G-t-butyl-S- indanol) 4,4'-methylene-bis(2,6-di-t-butylphenol), 2,2- methylene-bis(4-methyl-6-t-butylphenol). Preferred phenolic antioxidants are 2,6-di-t-butyl-4-methylphenol, 4,4- methylene-bis(6-t-butyl-5-indanol), and 2,2'-methylenebis(4-ethyl-6-t-butylphenol). Highly preferred are 2,6- di-t-butyl-4-methylphenol and 2,2'-methylenebis-(4-ethy1- G-t-butylphenol Metal corrosion inhibitors which may be used in the novel additive systems of this invention have been hereinbefore characterized by formula. These compounds include benzoguanamine and the alkyl substituted benzoguanamines. Benzoguanamine, itself, is preferably employed.

Although not wishing to be limited by any theory or mechanism by which stabilization is effected, it appears that the antioxidants employed in the novel additive system of the invention exert a complementary effect when used as herein prescribed. Amine antioxidants appear to be effective stabilizers against oxidation at temperatures in excess of about 150 0, whereas the phenolic antioxidants seem to be effective at temperatures below about 150 C. At temperatures in excess of about 150 C., in the presence of conventional antioxidants, thermal breakdown of many base fluids has been found to occur even in oxygen-free environments. It has now been found that certain compounds, herein referred to as thermolysis additives, effectively prevent such high temperature breakdown of the fluid.

Compounds which have been found to operate effectively as thermolysis additives are condensed ring compounds such as acridine, phenazine, quinizarin, alizarin, 2-benzylpyridine, and N,N-dibenzylpiperazine. Acridine is preferred.

The novel additive system of this invention contains from about 10 to 50 parts of amine antioxidant, from about 10 to 50 parts of phenolic antioxidant and from about 1 to 10 parts of the described metal corrosion inhibitor. In accordance with a preferred embodiment of the invention, the system also contains from about 1 to about 10 parts of thermolysis additive.

The additives are desirably employed in small amounts sufiicient to stabilize the fluids, i.e., the amine antioxidant and the phenolic antioxidant are desirably present in the fluid in small amounts sufficient to lend oxidative stability and the metal corrosion inhibitor is utilized in quantities sufficient to impart non-corrosive qualities. These desirable effects will be admirably achieved by utilizing the additive system containing the components in the above proportions, in small amounts sufiicient to impart superior resistance to oxidation and corrosion. Generally the additive system may be employed in amounts ranging from about 0.2 to about 12.0 percent by weight based on the base fluid. It is preferred that the said additive system be employed in amounts ranging from about 1.0 to about 6.0 percent by weight.

It is advantageous to heat the mixture in order to aid in the dissolving of the various components in the base fluid. It is pointed out that the novel lubricating compositions of this invention are formulated by mixing the components in the above defined proportions. The exact mechanism by which each of the additives functions is not precisely known. Therefore, upon mixing, the additives may in some measure, react with the base fluid resulting in a stable lubricant.

The novel additive system of this invention may be widely employed in a variety of synthetic lubricant base fluids. Generally the synthetic base fluids are those fluids of lubricating viscosity comprising compounds which consist essentially of carbon, hydrogen and oxygen, i.e., the essential nuclear structure is formed by these elements alone. Particularly contemplated are ester-type lubricants. For varying applications these ester lubricants may be utilized independently or together in blends i.e. with polyalkylene glycol derivatives depending on the characteristics desired in the finished lubricant. It has been found, in particular, that when base fluids comprising organic acid diesters and polyalkylene glycols or ethers of such polyglycols are utilized in conjunction with the additive system of this invention, lubricants may be provided which meet the rigid turboprop and turbojet lubricant requirements.

The ester-type lubricants contemplated can be simple diesters formed by the reaction of a dibasic acid with a monohydric alcohol, or polyesters prepared from polyhydric alcohols and polybasic acids in which reactive hydroxyl and/or carboxyl groups are not terminated, or polyesters prepared from polyhydric alcohols and polybasic acids in which reactive hydroxyl and carboxyl groups are terminated by reaction with monofunctional alcohols and/ or acids. The latter type, i.e., terminated polyesters, are frequently referred to as complex esters. In general, ester type synthetic lubricants are characterized as having viscosity properties of between 1 and 60 centistokes at 210 F. and an ASTM pour point of below about F.

Included among the suitable ester base fluids which may be used in the practice of this invention are:

(A) The dibasic acid esters which are represented by the formula ROOC(C H )COOR wherein n is an integer from 2 to 18 and preferably from 2 to 12, and wherein each R represents aliphatic or cycloaliphatic radicals, Which have from 5 to 18 carbon atoms.

Mixtures of different dibasic acids may be employed in the preparation of these diesters. Physical mixtures of the diesters may also be used. Illustrative examples or organic dibasic acids which the diesters may be derived include, for example, succinic, glutaric, adipic, pimelic, suberic, azelaic, seb'acic, hendecanedioic, dodecanedioic, brassylic, thapsic, octadecanedioic acids, and the like. The preferred acids are azelaic, adipic, sebacic, and suberic acids. The dibasic acids may be ialkyl substituted to obtain lower viscosities at lower temperatures, so long as the substitution does not raise the freezing point of the diester to over 0 F.

The alcohols used to form the diester of the acid may be branched or straight chain, saturated or unsaturated aliphatic or cycloaliphatic alcohols. The saturated alcohols are preferred. Typical alcohols which may be employed include 2-ethylhexanol, Z-ethylbutanol, cetyl alcohol, n-octanol, amyl alcohol, oleyl alcohol, 2-butyloctanol, methylcyclohexanol, dimethylcyclohexanol, and the like. Also useful are the Oxo alcohols such as isooctanol, isodecanol, tridecyl, alcohol, and the mixed branched chain nonanols which are prepared from the reaction of carbon monoxide and hydrogen upon olefins having a branched chain structure. Mixtures of alcohols may also be employed in the preparation of the diesters.

Representative synthetic diester lubricants which can be employed in conjunction with this invention include di (2-ethylhexyl )sebacate,

di Z-ethylhexyl) azelate,

di [mixed- Z-ethylhexyl, isodecyl) azelate, di isooctyl) azelate,

di 1-methylcyclohexylmethyl) sebacate,

di [mixed- (2-ethylhexyl, 2-propylheptyl) azelate, di 2,2,4-trimethylpentyl) sebacate,

di [mixed Z-methylpentyl, decyl) azelate, di( l-ethylpropyl) adipate,

di 3-methylbutyl) adipate,

di( 1,3 -dimethylbutyl) adipate,

di (2-ethylbutyl) adip ate,

di isooctyl adip ate,

di (undecyl) adip ate,

di (tridecyl) adipate,

di (isodecyl) adipate,

di- [mixed isooctyl, isodecyl) adipate,

di (tetradecyl adipate,

di (heptadecyl) adip ate,

di (2,2,4-trimethyl-pentyl) adipate,

di( 1-methylcyclohexylmethyl) adipate,

di 1-ethylpropyl) azelate,

di 3-methylbutyl) azelate,

di (2-ethylbutyl) azelate, di(1-ethylpropyl)sebacate,

di B-methylbutyl sebacate,

di( 1,3-dimethyl'butyl) sebacate,

di Z-ethylbutyl) sebacate,

di 2-ethylhexyl sebacate,

di [2- 2'-ethylbutoxy ethyl] sebacate,

di (undecyl) sebacate,

di tridecyl) segacate,

di (tetradecyl) seb acate,

di (heptadecyl) sebacate, di (Z-ethylhexyl) glutarate, di(undecyl) glutarate, and

di (tetradecyl) glutarate,

, formula:

(B). Esters of aromatic acids which correspond to the general formula:

Z(COOR scribed under (A) above.

Exampleswof acids, from which the aromatic esters can beipreparedincludeg phthalic, terephthalic, pyromellitic and. naphthalene-lA-dicarboxylic acid. The alcohols which are reacted with the aromatic acids are the same ,asithose mentioned under (A) above.

(C) Complex glycolcentered esters having the general 1 ring et-her linkages represented by the formula:

Raiofililolia whereinieachR individually represents an alkyl or cycloalkyl radical having from 4 to 24 carbon atoms, each R individually represents hydrogen atoms, methyl groups,

or ethylfgroups, and n represents an integer from 2 to 70.

Examples. of these glycol centered esters include dipropylene glycol diperlargonate, the diester of valeric acid and polyethylene glycol in which the latter has an average 1 molecular weight of 200, and the diester of 2-ethylhexanoicacid and polypropylene glycol in which the latter has an average molecular weight of 425.

(E) Esters prepared from a monobasic and an alkanepolyol corresponding to the formulae:

or it wherein R ifirepresents an alkyl group having from 1 to 8 carbon atoms, and n is an integer from O to 18.

1 Examples of alcohols which are reacted with aliphatic monocarboxylic acidsinclude trimethylolethane, trirnethylolpropane,11and pentaerythritol.

Itllisto beunderstood that the above classes of base .fluids are representative of fluids recognized in the art and are merely illustrative of some of the base fluids usefulin :this invention The complex esters have been described in the. art as well as in,U.S. PatentsyNos. 2,575,- 19.5.;.12,575,196; and 2,703,811.

(F) Alkyl terminated polyesters-These are complex polyesters prepared from polyhydric alcohols and polybasic acids wherein reactive carboxyl or hydroxyl groups are terminated by reaction with either monofunctional alcohols or, acidsii These esters are known in the art and are describedin U.S.-Patent No. 2,705,724. r

(GMHydroxyl terminated polyesters.-This class 0 compounds refers to those polyesters having free hydroxyl groups-ir1:the polymer chain which are not blocked or terminated by reaction with monofunctional or polyfunctional compounds. These compounds are known in the art and can be prepared by reacting a dibasic acid with a glycol or alkane diol as disclosed in US. Patent No. 2,929,786, or by reacting a dibasic acid with mixtures of polypropylene glycol and a 1,3-alkanediol.

In addition to the esters above, polyalkylene glycol derivatives are also stabilized by the novel additive system of the invention. These compounds may be represented by the formula:

Li. a J.

wherein each R represents hydrogen or an alkyl radical having from "l'to '12" carbon atoms, each R represents hydrogen atoms, methyl groups or ethyl groups, and n represents a positive integer from 2 to 70. R can be varied so as to provide homoand heteropolymers, i.e., polyethylene glycols, polypropylene glycols, mixed polyethylene-polypropylene glycols and also the mono alkyl ethers and dialkyl ethers of the above.

This class of compounds is well known in the art and the individual members of this class can be made in a variety of ways. Illustrative of the above class of compounds, as well as methods for the preparation of individual members can be found in US. Patents Nos. 2,293,- 868; 2,425,755; 2,425,845; 2,448,664; 2,520,611 and 2,520,612.

Although this invention involves the use of the novel additives package in various synthetic lubricants set forth above, particularly preferred compositions have base fluids comprising diesters of dibasic acids and blends of these diesters with monoalkyl ethers of polyalkylene glycols, particularly polypropylene glycol. Such compositions may contain 25 to percent by weight of a diester or of a mixture of diesters, 20 to 75 percent by weight of the said monoalkyl ether of a polyalkylene glycol, or mixtures of glycol ethers, and from about 1.0 to about 6.0 percent by weight of the novel additive system containing an amine antioxidant, a phenolic antioxidant and a metal corrosion inhibitor in the proportions hereinbefore set forth.

Highly preferred compositions contain 55 to 75 percent of the diesters, 45 to 25 percent of the glycol monoethers, and from about 1.25 to 4.5 percent of the said additive system.

In a preferred embodiment the above compositions containing the novel additive package of this invention may be advantageously complemented as hereinbefore disclosed, by the addition of a thermolysis additive which imparts to the lubricant compositions an ability to resist thermal breakdown at high temperatures. These thermolysis additives have been found to be necessary to meet requirements set forth in the British Ministry of Supply Specification for gas turbine lubricants.

It is to be understood that the novel lubricants of this invention can contain other well known additives. These additives can act as viscosity improvers, metal deactivators and anti-wear additives. For example, the polyacrylates may be employed as viscosity irnprovers. Disalicylidene-l,Z-diaminopropane may be used as the metal deactivator and tricresyl phosphate may be used as a lubricity and anti-wear additive.

Commercial turboprop aircraft lubricant specifications are described by the Allison Division Specification EMS- 34F and the British Ministry of Supply Specification, D. Eng. RD. 2487, Issue 3. Of particular interest in evaluating the fluids of this invention is the 347 F. corrosiontest fluid in a long cylindrical cell in the presence of weighed steel, copper, and lead specimens and maintaining the fluid at a temperature of 352 F. for 72 hours while purging with clean, dry air at the rate of liters (:0.5) per hour. The stability of the fluid is determined by measuring the viscosity and acid number change, observing the weight change of the metal specimens, and examining the fluid for the formation of insoluble material.

The British Ministry of Supply thermal stability test is described in Specification D, Eng. RD. 2487, Issue 3. In this test, a 100 ml. sample of test oil is placed in a long test cell, and after sparging with nitrogen gas for 20 minutes, is exposed to a temperature of 280 C. for six hours in the absence of air. After cooling, a sample of the fluid is taken for viscosity measurement. This operation is repeated for four consecutive 6 hour cycles or until the maximum permissible viscosity change is reached. The resultant change in viscosity at 100 F. of the oil shall not at any time exceed the limits to +10 percent. Thermal stabilities reported here were determined by the procedure described in the British specification except that test temperature was maintained at 282 C. rather than 280 C. as required in the specification test.

The following examples are illustrative.

8 Example 1 A blend was prepared having the following composinon: Percent by wt. Di-2-ethylhexyl azelate 58.8

Ucon lubricant LB625 1 31.36

Ucon lubricant LB-1715 2 7.84 2,6-ditertiary-butyl-4-methylphenol 1.0 Benzoguanamine 0.50

Percent by wt.

Di-Z-ethylhexyl azelate 54.2 Ucon lubricant LB-625 44.0 Phenothiazine 0.5 2,6-di-t-butyl-4-methyl phenol 1.0 Benzoguanamine 0.3

Properties of this product are shown in Table 1.

TABLE 1 Examples Allison EMS F Limits Kincmatg Viscosity, cs. at:

Corrosion and Ox Weight Change, mg./sq. crn.:

Viscosity Change at 100 F Total Acid N 0. Increase 5 to +12 1.5 (max.)

The following table will summarize various lubricating oil compositions and the effect of omitting one or more of the critical components of the additive system of this invention.

TABLE H Weight Percent Composition, Additives Corrosion-Oxidation Test 72 hrs. at 352 F.

Example Base Fluid Percent Metal Weight Change,

Viscosity mgJcm. 3 Amine Phenolic Corrosionlnhibitor Cha n% e,

Fe Cu Pb 3 32% Polyglycol AU 66.3% Di-2- 0.5 PHTZ 2 1.0 DBMP 3 0.2 BG 4 4.1 0.05 Nil Nil ethylhexyl azelate. 4 32% Polyglycol AU, 66% Di-2- 0.5 PHTZ 1.0 DBMP 0.5 BG 0. 99 0.03 -0.03 -0.04

ethylhexyl azelate. 5 32% Polyglycol AU, 67.0% Di-2- 1.0 BG 0.99 1.4 3.5 69.9

ethylhexy azelate. 7 32% Polyglycol AU, 67.5% Di-2- 0.5 PHTZ 21.5 Nil 0.16 l.0

ethylhexyl azelate. 8 44% Polyglycol BU 54.2% Di-2- 0.5 PHTZ 1.0 DBMP 0.3 BG 0.19 Nil 0.06 0. 32

ethylhexyl azelate. 44% Polyglycol BU, 53.7% Di-2- 1.0 PANA 1.0 DBMP 0.3 BG +4.9 Nil 0.12 7.1

ethylhexyl azelate. 44% Polyglycol BU, 55.5% Di-2- 0.5 PHTZ 11.7 0.03 0. 58 7.2!

ethylhexyl azelate. 44% Polyglycol BU, 2-eth- 1.0 PANA- 8.2 0.02 0.18 9.4

ylhexyl azelate. 30% monobutyl ether of poly- 1.0 PANA 1.0 MEBP 7 0.5 BG 7.2 0.007 0. 299 2. 38

propylene glycol (S.U.S. Vise, 1,145 at 100 F.), diethylhexyl sebacate. Corrosion-Oxidation Test Limits 5. 0 =l=0. 2 i0. 4

to +l2.0

4 Benzoguanamine. 5 Ucon LB 625.

6 N-phenylalphanaphthylamine. 1 2, 2,-methylene-bis (4-ethyl-G-t-butylphenol).

Itllcan beseen thatonly compositions which contained all three of the critical additives of this invention (Exampies 3,] 4, 8,. 9 and 12) met the critical specification for a lubricant as; defined by the Allison specification.

Othermlubricant blends were prepared having varying compositions. The compositions of these lubricant blends are setout in Table IIIbelow.

From the above tests it may be seen that Blend E containing antioxidants, metal corrosion inhibitor and acridine as a therrnoylsis inhibitor was the only lubricant to successfully pass both the thermal stability test and the corrosion oxidation test.

Specification tests on other useful thermolysis additives appears in Table VI below.

l Monobutyl ether of polypropylene glycol having a viscosity of 625 Saybolt Universal Seconds at 0 2 Monobutyl elt z her of polypropylene glycol having a viscosity of 1715 Saybolt Universal Seconds at 100? The follolvving Tables IV and V illustrate the results of the British Ministry of Supply thermal stability test and the corrosion-oxidation test made on each of the compositions prepared in Table I.

Iluid compositions:

TABLE.IV.THERMAL STABILITY (282 C.)

[Percent Viscosity Change at 100 F.: Test Time, hours] TABLE VI [Specification tests on potential thermolysis additives] Weight percent Di-Z-ethylhexyl azelate 66.9 UCON LB-1145 30.592

12 18 24 Phenylalphanaphthylamine 1.003 2,6-ditertiarybutyl-4-methylphenol 1.003 I213 1 Benzoguanamine 0.502 1. 4 7. 7 8. 8 +0: 74 ll): 10 5 :1 15] Test Additive Exposure Percent Vis' British Specification D. Time, hours cosity Change Eng. RD 2487, Issue.3 (1) 1 0.3 percent Acridine 24 1. 89 1 Limsts: 1D to 0%- 0.2 percent Phenazine (1% phenyibete- TABLE V naphthylamine inhibited 24 +1. 05 ['Corrosion'oxidation test, 72 hours at 352 F.] 0.3% Qmmzann 24 7.27 0.3% percent 2benzylpyrid 24 +3. 08 Pa t Percent Metal Weight 0.3 percent Alizarin 24 +0.18 f Change rngJcm. 0.3 percent N ,N-di nzy g zylpiperazine 24 +1. 0 Change BlendA 11.7 BlendB- 19.3 1333 The following table demonstrates further how the addi- Blend EL- +111 tion of acridine to t ad iv 352 F. Corrosion Oxidation he dlt e systel'll lmpmves 1W Test Limits -5 to 12 ioz +0.4 =|=1.0 of various lubricants under the conditions of the British Ministry of Supply Test.

TABLE VIT.EFFECTIVENESS 0F ACRIDINE IN IMPROVING THERMAL STABILITY [Test Method; Turboprop lubricant specification as per British Ministry of Supply Specification D. Eng,

P..D. 2487 Issue 31 I Percent Flu1d Composition Additive Hours at Change in Viscosity 74% di(isodecyl)adipate 2.57 Additive Packa eA* 24 3 ?E%E FI 1 1 t 7 Add P k g 6 6 0 i iso ecy ,ar ipa e 2.5 itive ac ageA 21 -0.9 26% UCON LB-625 0.3% Acridine Di(2'ethylhexyl)sebacate 2.5% Additive Package A 24 +15. 46 Di(2-ethylhexyl)sebecate 2.55:? iddgzivc Package A".-. 24 +2. 67

0. 0 cri inc. 70% di(2-ethy1hexyl)sebacate 1% phenylalphanaphthylamine 24 -3. 6 UCON LIZ-1145 1% 2,2-methylene-bis(4-ethyl-6-ditertiary butyl phenol). 0.5% benzoguanarnine. 70% d1(Z-ethylhexyl)sebacate-.- 1% phenylalphanaphthylamine 24 -0. 19 30% UCON LB-1145 1% 2,2-methyIene-bis(4-ethy1-6diteitiary butyl phenol). 0.5% benzoguanamine. 0.3% Acridine. UCON LB-625 2.5% Additive Package A.-- 6 --21 UCON LB-625 2.5% Additive Package A.-- 18 -29. 4

0.3% Acridine.

Additive Package A: 50 parts phenylalphanaphthylamine; 50 parts 2,6-ditertiary-butyl-4-methy1 phenol;

25 parts benzoguanamine.

What is claimed is:

1. A novel additive system for use in synthetic ester and glycol lubricants which comprises from about to about 50 parts by weight of a compound selected from the group consisting of phenothiazineand N-phenylalphanaphthylamine, from about 10 to about 50 parts by weight of 2,6-di-t-butyl-4-methylphenol and from about 1 to about 10 parts by weight of benzoguanamine.

2. A non-corrosive, non-oxidative lubricant composition which comprises a lubricant base fluid which consists essentially of synthetic fluid of lubricating viscosity selected from the group of organic dibasic acid esters, the monoalkyl ethers of polypropylene glycol, and mixtures thereof, and from about 0.2 to about 12 percent by weight, based on the base fluid, of the additive system of claim 1.

3. The lubricant of claim 2 which contains from 1 to 10 parts by weight acridine based on the said additive system.

4. A non-corrosive, non-oxidative lubricant composition which comprises a lubricant base fluid which consists essentially of from about 25 to about 80 percent by weight of at least one diester of a dibasic carboxylic acid and from about 20 to 75 percent by weight of a monoalkyl ether of a polyalkylene glycol and from about 1.0 to about 6.0 percent by weight of an additive system which comprises from about 10 to 50 parts by weight of a compound selected from the group consisting of phenothiazine and N-phenyl-naphthylamine, from about 10 to 50 parts by weight of 2,6-di-t-butyl-4-methylphenol and from about 1 to 10 parts by weight benzoguanamine.

5. The non-corrosive, non-oxidative lubricants of claim 4 which contains from about 1 to 10 parts of acridine based on the novel additive system.

6. A non-corrosive, non-oxidative lubricant composition which comprises a synthetic lubricant base fluid which consists essentially of from about 25 to about 80 percent of at least one dialkyl ester of a dibasic carboxylic acid selected from the group of adipic, sebacic and amlaic acid, and from about 20 to about 75 percent of a monoalkyl ether of polypropylene glycol, and from about 1.0 to about 6.0 percent by weight of an additive system which comprises from about 10 to about parts by weight of a compound selected from the group consisting of phenothiazine and N-phenyl-naphthylamine, from about 10 to about 50 parts by weight of 2,6-di-t-butyl-4- methylphenol, from about 1 to 10 parts by weight of benzoguanamine and from about 1 to 10 parts by weight acridine.

7. A novel additive system for use in synthetic ester and glycol lubricants which comprises from about 10 to about 50 parts by weight of a compound selected from the group consisting of phenothiazine and N-phenylalphanaphthylamine, from about 10 to about 50 parts by weight of 2,6-di-t-butyl-4-methylpheno1, from about 1 to about 10 parts by weight of benzoguanamine and from about 1 to about 10 parts by weight of a thermolysis additive selected from the group consisting of acridine, phenazine, quinizarin, alizarin, 2-benzylpyridine, and N,N'-dibenzylpiperazine.

References Cited by the Examiner UNITED STATES PATENTS 2,316,587 4/1943 Irigai g 25250 2,441,849 5/1948 Sexton et al. 252390 2,448,664 9/1948 Fife et a1 260-615 2,520,733 8/1950 Morris et al. 25252 2,672,448 3/ 1954 Newnan 25252 2,714,057 7/1955 Chenicek 25250 2,734,807 2/ 1956 Chenicek et al. 252390 2,786,080 3/1957 Patton 25247.5 2,862,976 12/1958 Dubbs et al 25252 2,898,299 8/1959 Lowe 25252 2,944,973 7/ 1960 Langer et al 252565 3,026,263 3/1962 Arimoto 25250 3,047,501 7/1962 Brook et a1 25250 3,049,493 8/ 1962 Young et al 25256 3,053,768 9/1962 Cupper 25256 X 3,093,585 6/1963 LOW et al 25251.5

DANIEL E. W Y MAN, Primary Examiner.

P. P. GARVIN, Assistant Examiner. 

1. A NOVEL ADDITIVE SYSTEM FOR USE IN SYNTHETIC ESTER AND GLYCOL LUBRICANTS WHICH COMPRISES FROM ABOUT 10 TO ABOUT 50 PARTS BY WEIGHT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHENOTHIAZINE AND N-PHENYLALPHANAPHTHYLAMINE, FROM ABOUT 10 TO ABOUT 50 PARTS BY WEIGHT OF 2,6-DI-T-BUTYL-4-METHYLPHENOL AND FROM ABOUT 1 TO ABOUT 10 PARTS BY WEIGHT OF BENZOGUANAMINE. 